freewill, it sounds like your son and his ex are going for couples therapy. It is very typical that insurance does not cover couples sessions. Check your plan. Most plans only cover therapy if there is only one person present. This is the case for 4 different plans I have had access to. My T, who is a family therapist, has agreed this is his experience--family therapy of any flavor usually not covered.

Your son and his ex will probably just have to pay the full, out of pocket rate if they want to see your T together.